Plural lamp ballast



Sept. 18, 1962 A, B. ELLIOTT, JR

PLURAL LAMP BALLAST o .FZ- z/ 7 L @Y /H ms. m AMW L /mmw i E005 .Eff H H United States Patent O 3,054,930 PLURAlL LAMP BALLAST Andrew Byron Elliott, lr., River Forest, lll., assigner to Jefferson Electric Company, Bellwood, Ill., a corporation of Delaware Filed May 18, 1960, Ser, No. 29,834 4l Claims. (Cl. 315-138) This invention relates to a plural lamp ballast, and in particular, to an improved starting circuit -for the same.

The standard two-lamp series ballast provides a leading secondary circuit, a condenser being connected in series with the two lamps to provide capacitive ballasting. The load circuit is energized by a leakage reactance transformer either of the insulated or auto type.

The characteristic of a gaseous discharge device, such as a fluorescent lamp, is that the starting voltage required is not only much greater than the operating voltage, but it is also greater than the vector sum of the voltage drops across both the lamp and the ballasting impedance. Therefore, the transformer must be provided with suicient additional turns as tot provide the desired starting voltage on open circuit.

Various arrangements have been proposed for reducing the over-all starting voltage so as to permit a reduction in turns; the standard circuit now in use is a sequence start circuit which includes a shunt condenser connected across one of the lamps. Thus, the full transformer voltage is applied to the number one lamp to star-t it, and then the voltage drop across the starting condenser is utilized to start the number two lamp.

In such an arrangement, it has been the practice that the voltage drop across the starting condenser is less than the open circuit voltage of the transformer which is applied to start the number one lamp. This is due to the fact that there are other impedances in the load circuit, such as the operating condenser, and also the resistance of the number one lamp, with the result that the Voltage drop across the starting condenser will represent only from about 70% to 90% of the open circuit voltage.

Therefore, according to the prior art practice the circuit is designed with respect to the number of turns required to create the desired voltage drop across the starting condenser, which means that the open circuit voltage is greater than that required for starting the number one lamp.

It is an object of my invention to provide a starting circuit in which the starting voltage applied to the number one lamp is lower than that of the prior art device mentioned above.

According to my invention, I have found that satisfactory starting of the number one lamp at a lower Voltage can be obtained if the starting condenser is shunted across both the number two lamp and the primary. As a result, only the secondary voltage is applied to the number one lamp, whereas the condenser drop plus the primary Voltage is applied to the starting of the number two lamp. As a result, the starting voltages are more nearly equalized than in the case of the prior art arrangement.

The advantages of my invention become more apparent when the arrangement is applied to a three or four lamp ballast since, in such situations, the turn ratio required for operating three or four lamps in series is such that the open circuit voltage of the secondary is necessarily more than sufficient to strike the number one lamp, and the starting voltages available, according to my invention, for the number two, three, and four lamps are in general as great or greater than the available starting voltage for the number one lamp.

Another object of my invention is to provide an improved ballast for operating three or four or more lamps.

A still further object is to provide a plural lamp ballast 3,954,930 Patented Sept. 18, 1962 ice requiring lower voltage ratings for the lead wires and lamp holders than in the case of comparable ballasts of the prior art.

With reference now to the drawings in which like reference numerals designate like parts:

IG. l is a diagram showing the application of my invention to a two-lamp ballast;

FIG. 2 is a diagram showing the application of my invention to a four lamp ballast; and

FIGS. 3, 4 and 5 are diagrams illustrating the operation of the circuit shown in FIG. 2.

With reference now to FIG. l, the ballast includes a transformer having a primary winding 10 which is connected to line 11, and a secondary winding 12, the two being connected in autotransformer relationship and wound on a suitable core structure, not shown, which provides a leakage path between the primary and secondary windings, this ybeing in accordance with standard practice in the art.

The transformer is provided with a plurality of filament windings 30, 31, 32 and 33, closely coupled to the primary, for the lamp filaments of rapid start lamps, this also being a standard practice.

The primary and secondary windings 10` and 12 are connected in a series circuit which includes an operating condenser 13, the number one lamp #1, and the number two lamp #2. As shown in FIG. l, `only the #l lamp is connected across what might be said to be the output side of the transformer, by leads 14, 15 whereas the #2 lamp and the operating condenser are connected between the windings 1t) and 12 on either side of a junction point 16. The operating condenser 13 is connected between the junction point 16 and the secondary winding 12 whereas the #2 lamp is between the junction 16 and the primary winding 10. A starting condenser 17 is connected ybetween junction point 16 and a junction point 1S which is located in the lead 15 between the `#1 lamp and the primary winding 10. Thus, the starting condenser 17 is shunted across the #2 lamp and the primary 10 so as to provide a `series circuit which is energized only by secondary winding 12 and which includes elements #1, 17 and 13.

The secondary winding 12 is designed so as to provide an open circuit voltage which is in excess of the `starting voltage of the `#C1 lamp. In operation, as soon as the primary 1t) is energized, the open circuit voltage of the secondary winding 12 will `strike the `#1 lamp. The starting condenser 17 oiTers a relatively high impedance with respect to Ithe total impedance of circuit 13, 12, #1, 17, with the result lthat the major portion of the secondary voltage is represented by the voltage drop across the starting condenser 17. The sum of this voltage drop and a component of the line Voltage is suiiicient to strike the #2 lamp.

In the four lamp ballast shown in FIG. 2, the corresponding reference numerals are used for corresponding parts, but the circuit includes a #3 llamp and a #4 lamp, between which are junction points 20 and 21.

The conductor extending between the rst starting condenser 17 and the junction point 16 is designated by the reference number 22, and is provided with a junction point 23. A second starting condenser 25 is connected between junction points 20 and 23, and a third starting condenser 26 is connected between junction points 20 and 21.

As `soon as the primary winding 1t] is energized, the full open circuit voltage of the secondary winding 12 is applied directly to `the #1 lamp, as in the case of FIG. 1.

FIGS. 3, 4 and 5 illustrate the operation of the circuit during the starting of the #2, `#3 and #4 lamps.

In each of these gures, the established circuit is shown in full lines, and the circuit which includes the neXt lamp to start is shown in broken lines, other circuit elements and conductors being omitted for the sake of clarity.

' According lto FIG. 3 the voltage applied to the #2 lamp is the sum of a component of the4 line voltage plus the voltage drop across the first starting condenser 17. It will be understood, of course, that prior to the establishment of a circuit through the #2 lamp and through the second starting condenser 2S that there is no voltage drop across the starting condenser 25.

According to FIG. 4, the starting voltage applied to the #3 lamp is essentially the voltage drop across the second starting condenser ZS.

According to PIG. the starting voltage applied to the #4 lamp is the voltage drop across the second starting condenser 26.

Let it be assumed, for the purpose of discussion, that each one of the `starting condensers 17, 25 and 26 have a capacity of .09 mfd. which represents an impedance of approximately 29,000 ohms at 60 cycles. Therefore at `a current of substantially .016 amp., which might obtain in the solid line circuit shown in FIG. 3, the voltage drop across the first starting condenser 17 would be of the order of 465 volts which, when added to a line voltage which is about 60 degrees out of phase with the condenser 17, would produce about 540 volts which -is more than sufficient to `strike a 72-T-l2 type S00 ma.

application, Serial No. 647,771 filed March 22, 1957.

This type of core provides a relatively loose coupling starting condensers 17, 25 and 26 are each .O9 mfd.

The lamps 1, 2, 3 and 4 are 72-T-12 type 800 ma. rapid start lamps having a rated operating voltage of 113 volts at .800 amp.

Suitable lament windings, not shown, are provided as in the case of FIG. l.

Under starting conditions, the voltage drop across the #1 lamp is of the order of two or three times the operating voltage, with the result that the total circuit impedance is of the order of 34,000 ohms. The striking voltage developed by the secondary winding 12 under these conditions, about 565 Volts, is suficient to strike the #1 lamp, and also to provide a voltage drop across the first starting condenser 17, which when added to a component of the primary voltage is suicient to sta-rt the #2 lamp.

In the circuit condition shown in FIG. 4, the total impedance of the solid line circuit is greater than the solid line circuit of FIG. 3 due to the impedance of #2 lamp. However, the series circuit now includes the primary voltage which is more than suicient to compensate for the increase in circuit impedance caused by the inclusion of the #2 lamp in the starting circuit. As a result the current is enough greater than that of the FIG. 3 circuit as to provide a drop across the second starting condenser 25 suiiicient to start the #3 lamp.

Similarly, the voltage drop across the third starting :condenser 26is sufficient to start the #4 lamp.

One advantage of the present arrangement over that of the prior art is that the leads 14 and 15, which connect the `iii-'1 lamp to the secondary 12, together with the lamp holders, need have only a 600 volt rating,

whereas in the prior art arrangement for a four lamp ballast, a 1000 volt rating is required for the lamp leads. Similarly, only a 600 volt rating is required for lead 19 connecting the primary 10 and the #2 lamp, and for the lamp leads through junction points 20, 21 and 16, together with their associated lamp holders.

Although only preferred embodiments of my invention have been shown and described herein, it will be understood that various modifications and changes may be made in the constructions shown without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A plural lamp ballast comprising a high leakage reactance autotransformer including primary and secondary windings, a plurality of gaseous discharge devices connected in series circuit with each other and with said primary and secondary windings in order to provide a series operating circuit, an operating condenser included in said series operating circuit, a starting condenser, and means connecting said starting condenser in a shunt circuit across said primary winding and all except one of said gaseous discharge devices.

2. A plural lamp ballast comprising a high leakage reactance transformer including spaced primary and secondary windings and means connecting the same to provide an autotransformer connection, leads for connecting a gaseous discharge device across both of said windings, one of said leads being connected to said primary Winding, a first junction point in said connecting means, a second junction point in said primary connected lead, a starting condenser connected between said two junction points to provide a series starting circuit which includes said secondary Winding and not said primary Winding, said connecting means including means for connecting a second gaseous discharge device between said primary winding and said first junction point so as to provide a series operating circuit which includes both of said windings, and an operating condenser connected in series circuit with said secondary winding and being common to both of said series starting and series operating circuits.

3. A plural lamp ballast comprising a high leakage reactance transformer having a primary winding and a secondary winding adapted for energization of a plurality of gaseous discharge lamps in series circuit, means connecting said primary and secondary windings to provide an autotransformer connection, lead means connecting a number one lamp across said primary and secondary windings, said autotransfor-mer connecting means including a number two lamp, a junction point, and an operating condenser, said number two lamp being located between said primary winding and said junction point, and said operating condenser being located between said rst junction point and said secondary winding, a second junction point located in said lead means between said number one lamp and said primary winding, and a starting condenser connected between said irst and second junction points, the impedance of said starting condenser being of the order of ten or more times as great as the impedance of said operating condenser, whereby said starting condenser is shunted across both said number two lamp and said primary winding to provide a series starting circuit which includes said starting condenser, said operating condenser, said secondary winding and said number one lamp so that the starting potential applied to said number one lamp is only the potential of said secondary winding, and whereby the starting potential applied to said number two lamp is the voltage drop across said starting condenser plus a component of the voltage across said primary winding.

4. A plural lamp ballast for energizing three or more gaseous discharge devices including a high leakage reactance autotransformer having primary and secondary windings, a number one gaseous discharge device con- 5 nected across said primary and secondary windings, a plurality of other gaseous discharge devices connected in series between said primary and secondary windings, an operating condenser connected in series with said secondary winding and said number one gaseous discharge 5 device, a irst starting condenser connected across said primary and said other gaseous discharge devices to provide a series starting circuit which includes an operating condenser, said secondary winding, said number one gaseous discharge device and said rst starting condenser, and 10 second starting condenser means connected across al1 eX- cept one of said other gaseous discharge devices and including one starting condenser for each gaseous discharge device which is shunted by said second condenser means.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain Oct. 29, 1952 

